1. Field of the Invention
This invention relates to a display device, specifically to a display device that performs a display by illuminating an object having a display surface such as a vehicle-mounted instrument.
2. Description of the Related Art
The vehicle-mounted instrument such as a speedometer and a tachometer is structured as an electronic display device, and mounted in an instrument panel in front of a driver's seat. Such a display device will be described hereafter referring to the drawings. FIG. 9A shows a vehicle-mounted display device according to a prior art. FIG. 9B shows a cross-sectional view of a section B-B in FIG. 9A.
A display device 100 that is mounted in an instrument panel 10P is composed of an instrument 110 that is an illumination object having a display surface and a light source 120 such as a light bulb placed on a backside (a side not facing an observer), as shown in FIG. 9A and FIG. 9B. A speedometer display 111, a tachometer display 112 and other displays 113 are placed in the instrument 110. These displays are made of transparent material or a transmission type liquid crystal panel. Each of the displays is visually recognized by that the light from the light source 120 passes through each of the displays and travels toward the observer.
Technologies mentioned above are disclosed in Japanese Patent Application Publication No. 2002-257602.
However, there is a problem that the display device 100 described above takes a large space to be mounted in the instrument panel 10P, because the light source 120 such as the light bulb is placed in the instrument 110 on the side not facing the observer. Also, there is a problem that brightness within the display surface is inhomogeneous to reduce the viewability, because a distance between the light source 120 and the instrument 110 is not uniform. Also, when the display in the instrument 110 is provided with a pointer, there is a problem that the structure of the display device 100 becomes complicated, because an additional illumination device dedicated for the pointer is required.